The multiple forms of monoamine oxidase (MAO) are being studied using electron spin resonance techniques (ESR). The catalytic (and binding) site(s) of the enzyme will be investigated in situ in the membrane of brain mitochondria as well as in human blood platelets from patients suffering from schizophrenia or depressive illness. Using spinlabeled probes (substrates and inhibitors) of varying size, the nature of the active site will be assessed. The relationship of the membrane to the conformational site of the enzyme protein will be investigated by studying the local lipid domain usng spin-labeled lipid probes. Specific characteristics, both static and dynamic properties (delta F, delta H, delta S, transition temperatures, etc.) of the MAO multiple forms will be investigated in both brain and platelet preparations. These characteristics of MAO will be measured in platelets derived from mentally ill individuals and will be compared to normal controls.